December 17th, 2020
Knowing which linear motion system to choose can be a difficult task and choosing the right one is important so that you are not left disappointed with the performance of the system. Each type of linear motion system has its pros and cons, so read this helpful guide to find out which one you should choose.
Generally, there are two different types – roller and plain bearing linear motion systems. Let’s have a look at the important things to consider when choosing the right one: load and adjustment.
Getting the right adjustment force for the user is important. Have you ever tried to adjust the seat in your car and you’ve either flown back or hardly been able to move it? This is a result of getting the adjustment force wrong!
The adjustment force is all about physics! The friction that the roller bearing, or linear slides generate and the load applied, give the resulting adjustment force. Roller bearings have much lower friction rates than plain bearings (about 10 times lower!) and are therefore the correct choice if you are going for minimum adjustment effort. Of course, the actual values you can achieve vary a lot depending on the materials you use, the grease and the operating temperature.
It’s important when designing a linear motion system to get this balance of load, friction and adjustment effort right.
As an example, if the system must handle heavy loads and the adjustment should be as low as possible, linear roller systems are the perfect choice (100kg load will result in adjustment force of roughly 10N).
In applications without high loads, linear slide bushings may be a better option.
Ball bearings are designed to have no slip, so the outer and inner rails are linked to each other. During the motion of the system, the steel ball in the linear ball bearing rotates towards the outer and inner rail. This means that the possible adjustment length of linear roller systems depends on both, the length of the inner and outer rail. Linear slider systems have an advantage here as the adjustment length only depends on the length of the outer rail as they are fixed to the inner rail.
Linear slider systems are self-lubricating. During operation, small particles of PTFE are worn of the linear slider and stick to the rails. This in combination with the low coefficient of friction of PTFE leads to a self-lubrication effect where no grease is needed. PTFE elements work like a seal which keeps the sliding surface clean. Linear sliders work perfectly in harsh environments. As the PTFE elements come with a thick layer, they provide enough lubrication for the whole lifecycle what makes them maintenance free.
Linear rollers require grease as a metal to metal contact comes with several challenges. Grease avoids corrosion, reduces noise and reduces the coefficient of rolling but collects dust and particles from the environment. In most cases, linear ball bearings come with enough grease for the whole lifecycle. But this is a potential topic during maintenance.
When you are specifying different systems, it’s often easy to overlook the hidden aspects of producing those parts.
Roller bearing type sliding systems are ubiquitous in the industry, but they also come with their fair share of manufacturing challenges. The fit between each of the tracks and ball bearings is critical to get the right effort – too tight and the adjustment can be too high, and too loose could lead to rattle and noise.
Because of this, special attention needs to be paid to the tolerances of the tracks and balls. Often there is some matching process done (where all the components are measured one by one, then matched to each other to give the perfect fit).
In a linear slider, firstly, there are fewer sliding elements than in a roller type one, making the assembly of them easier. Secondly, due to the inherent properties of the PTFE and spring elements, they automatically compensate for the tolerances of the rails. This means that the tolerance of the rails doesn’t need to be so tight, saving some cost. Steel balls work better with point contact which leads to Brinelling, whereas slider requires line- or surface contact which avoids Brinelling.
Our engineers will work in close collaboration with you, making sure that your system is robust and reliable. Contact us today to discuss your custom-made linear sliders. For further information on our sliding bearing technology visit the NORGLIDE® Bearings product page.